Recently, hybrid vehicles and electric vehicles have been of great interest as environment-friendly vehicles. The hybrid vehicle is a motor vehicle including, as its motive power sources, a conventional engine and additionally a motor driven by a DC power supply through an inverter. Specifically, a motive power is obtained by driving the engine, and a motive power is also obtained by converting a DC voltage from the DC power supply into an AC voltage by the inverter and rotating the motor with the AC voltage generated by the conversion.
The electric vehicle is a motor vehicle including as its motive power source a motor driven by a DC power supply through an inverter.
For the hybrid vehicle or electric vehicle, a control apparatus driving and controlling the motor is proposed for example in Japanese Patent Laying-Open No. 2001-145381. The control apparatus determines the number of revolutions of the motor from the rotor position detected by a resolver, adjusts the phase of a rectangular-wave signal which is output to each of u, v and w phases of the motor based on the determined number of revolutions, and thereby controls the output torque of the motor.
Thus, in a motor control routine repeatedly performed at predetermined time intervals, the controller first reads the electrical angle of the rotor detected by the resolver, and uses the read electrical angle to calculate the number of revolutions of the motor. Subsequently, the controller determines the phase of the rectangular wave signal based on the calculated number of revolutions of the motor. According to the determined phase, a switching element for the u, v and w phases each is switched to control the torque of the motor.
Regarding the above-described control apparatus for the motor, however, in the case where a drive wheel skids for example to cause the number of revolutions of the motor to sharply increase, a large difference could be generated between the number of revolutions of the motor calculated from the read electrical angle and the number of revolutions of the motor while the output torque of the motor is being controlled. This difference is increased due to for example a delay in calculation of the controller and a delay in communication between the controller and the resolver.
In other words, due to the sharp increase of the number of revolutions of the motor, the number of revolutions of the motor while the motor is actually driven and controlled according to the set output torque could be significantly larger than the number of revolutions used for setting the output torque of the motor.
In this case, if the motor is driven in a power running mode, the motor-consumed power (torque×number of revolutions) which is expected when the motor output torque is set is exceeded by the motor-consumed power while the output torque is actually controlled. As a result, an excessively large electric power could be drawn from the DC power supply.
If the motor is driven in a regenerative mode, the motor-generated power which is expected when the motor output torque is set is exceeded by a motor-generated power while the output torque is actually controlled. As a result, an excessively large electric power could be given to the DC power supply.
As seen from the above, regarding the output torque control by means of the calculated number of revolutions of the motor, it is difficult to perform control adapted to a sharp change of the number of revolutions. Therefore, a problem arises that the DC power supply is overcharged or overdischarged to an extent exceeding the input/output power limit.
The present invention has therefore been made to solve the above-described problems. An object of the invention is to provide a control apparatus for a motor that can perform drive and control following a change of the motor operating state and that can prevent the power supply from being charged or discharged with an excessive power.